1. Field of the Invention
The present invention relates to a battery condition-detecting apparatus and a battery condition-detecting unit for detecting the battery condition of a battery set which comprises individual batteries connected in series. In particular, the present invention relates to a battery condition-detecting apparatus and a battery condition-detecting unit preferably used for a battery set which is carried, for example, on an electric vehicle or a hybrid vehicle.
2. Description of the Related Art
An electric vehicle is provided with a motor as a running driving source, and a hybrid vehicle is provided with a motor and an engine as running driving sources. In such vehicles, a battery is carried and used as a power source for the motor.
In such a case, the battery practically comprises a plurality of individual batteries each having about 1 to 12 V. The individual batteries are connected in series so as to provide an appropriate voltage to drive the motor. The individual batteries are utilized in a form of battery set which is designed to be capable of generating a high voltage appropriate to drive the motor.
The battery is highly temperature-dependent. Therefore, when the battery charge or discharge is controlled, it is necessary to detect and control the temperature of the battery, in addition to the detection of the voltage of the battery and the inflow or outflow current with respect to the battery.
The voltage and the temperature of the battery have been hitherto detected, for example, as follows. That is, the high voltage as the terminal voltage is detected (measured) in the state of battery set, and the temperature is detected in the state of battery set.
However, if any of the individual batteries for constructing the battery set has any trouble during the process for detecting the terminal voltage and the temperature in the state of battery set as described above, a problem arises in that it is difficult and time-consuming to specify the troubled individual battery.
In order to solve this problem, the following system may be conceived. That is, detection lines are drawn from points of serial connection of the respective individual batteries which constitute the battery set. The respective detection lines are switched by using a relay to lead them to ECU (electronic control unit) so that the battery voltage is detected.
However, when such a system is adopted, it is necessary to use one which is resistant to high voltage, as the relay for switching the detection lines. Therefore, a problem arises in that the size of the relay is large and the cost is expensive as well.
Further, it is also necessary to use a large number of the detection lines to serves as the lines to draw the voltage from the battery set. Furthermore, each of the detection lines is a thick electric wire which is resistant to high voltage. Therefore, another problem arises in that the harness (wiring arrangement bundle) becomes fat, and it is difficult to practically provide such a harness on a vehicle or the like.
A technique for detecting the voltage of each of the individual batteries for constructing the battery set is exemplified by one disclosed in U.S. Pat. No. 4,394,741. However, this patent document describes nothing about any technique relevant to the problems described above.